The final refining of several metals, such as, for example, copper, is carried out with electrolysis. This electrorefining process uses dissolvable anodes which are produced by casting molten metal into anode molds. The formed anodes are immersed in the electrolytic cells and are suspended therein by “lugs” formed at the upper end of the anode. On top of the first side wall of each cell, there is a busbar, and on top of the second side wall there is provided insulation. The anode lugs rest on the busbar and the insulation. The high electric current in the cell proceeds via the contact with the busbar and the anode lugs.
A cathode of another metal, such as stainless steel is also immersed in the cell, and also has lugs which rest on a second busbar and insulation. During the electrorefining process, metal from the anode dissolves into the electrolytic, and is then subsequently deposited onto the anode in a more purified state. Through this operation, the purity of the metal can be raised to 99.9% or higher, and the contaminant materials present in the original cast anode typically settle to the bottom of the cell where they can be removed. The electrorefining operation, utilizing electrolytic cells, is well known in the art, and a detailed discussion of that process is outside of the scope of the present invention.
However, it is to be noted that a typical metal anode is commonly approximately 1 meter square in size, and can be anywhere from 2 to 10 cm, or more, thick. The anode is usually formed by casting molten metal into a suitable mould and then allowing the metal to cool and solidify. Alternatively, the anode can be cut from a continuous casting of material.
Typically, an anode can weigh between 200 and 400 kg, and thus, handling and movement of the anode during anode preparation can be difficult. Further, in a large scale metal mine, the number of anodes needed can also be fairly large. For example, in some mines, over a million anodes are required in a given year.
As such, it is necessary to have high anode production rates. Initially, formation of the raw anode is commonly done by casting the molten metal material into horizontal moulds provided on a casting wheel, or the like, or by having a rotating series of vertical moulds. Again, though, the actual techniques for the production of the raw metal anodes are well known in the art, and therefore, are also outside of the scope of the present invention.
However, while a large number of raw metal anodes can be prepared using the prior art techniques, in order to ensure optimal efficiency in the electrolytic cell, it is still necessary to conduct several anode preparation operations on the raw anode, as cast, in order to provide an anode suitable for use in the electrolytic cell.
For example, in order to gain maximum electrical contact and consequently minimum electricity losses, the bottom surfaces of the anode lugs are commonly milled, smoothed and/or cleaned in order to be flat and perpendicular to the anode end surface. This is necessary to maximize contact with the busbar and ensure that the anode hangs substantially perfectly vertical in the electrolytic cell. The lugs might also need to be bent and/or straightened to be parallel to the front or back anode surfaces.
Further, the anodes surfaces are commonly rolled or hydraulically pressed in order to minimize thickness variations between anodes and/or across the surface of the anode itself. These variations in the anode thickness might be caused by acceleration or deceleration of the casting wheel, having a non-level casting mould, or having a heat-warped casting mould.
Further still, the surface of the anode may be ground or milled in order to provide patterns on the anode that will reduce the chances of breakage of the anode during handling or use, or to provide patterns which can influence the ultimate rate and anode dissolution profile. The anode might also be milled so as to provide a thinner top section that will allow the anodes to be moved closer to one another as the anode dissolves in the electrolytic process.
Alternatively, or additionally, a thicker section in the upper portion of an electrode might be provided on the anode, between the lugs. This thicker section may be necessary to ensure that there is sufficient metal left after the electrorefining process in order to prevent buckling between the lugs as the remaining anode is removed from the electrolytic cell. If an anode buckles or breaks as it is being removed, it can present a serious safety hazard and/or can cause significant damage to equipment.
Still further, it may be necessary to grind or mill off extraneous casting “fins” or “flash” material formed at the edges of the mould. Other processes steps might also be required depending on the specific electrorefining process utilized.
As such, it is clear that processing of the raw, cast anode prior to use is typically desirable in order to maximize the efficiency of the electrolytic cell.
Currently, after casting, the anodes are commonly hung on a rack in a vertical fashion by their lugs. They are then processed by being moved on a conveyor system from treatment station to treatment station where the various operations are individually conducted on the vertical anodes. This anode processing technique is typically designed so as to be capable of handling 200 to 300 anodes per hour (APH). However, given the production rates of some mines, these anode treatment process rates are inadequate, and therefore two or more treatment lines may be required to meet production needs.
Higher anode production capacity processing designs are also currently known. These high capacity (greater than or equal to 450 APH) anode preparation systems are available in two different formats, namely linear systems and carousel systems.
In a high capacity linear system, the anodes are moved along a track while hanging in a vertical orientation. They are also transferred in a vertical orientation, laterally between operation stations. The linear system is typically chain driven and, in practice, is limited to a capacity of 500 APH.
Additionally, in a linear system, clamping of the anodes is less positive, and is more prone to anode mis-positioning as the chain wears. As such, the linear process can be inaccurate. Further, when installed, the linear system is fairly large so that is is typically delivered in sections and requires significant millwrighting during installation. The linear system also typically requires connection to an external hydraulic system. Further, the linear system is very rigid, in that the anodes incoming and outgoing must maintain the same vertical orientation throughout the process.
In the high capacity carousel systems, the anodes are transferred from the feed rack to various processing operation stations which are provided in a carousel arrangement. However, again, the anodes are processed while being maintained in a vertical orientation. As such, the anodes are maintained in a vertical orientation as they pass through each operation around the carousel, and then placed back onto an output rack while still in the vertical orientation.
To allow room for the processing equipment at each operational station on the carousel, the anodes must be kept at a distance from the centre of the carousel. As such, this required distance from the centre of the carousel provides significant mechanical disadvantages, as will be discussed hereinbelow. Further, existing carousel systems are also fairly large systems which again are shipped as a number of separate assemblies to be field installed. Again, this typically requires a significant amount of field millwrighting, and commonly the connection of hydraulic services. In practice, the carousel systems are generally limited to 450 APH.
To overcome the difficulties of known high capacity anode treatment processes, it would advantageous to provide an improved process and apparatus to facilitate the processing of metal anodes in order to prepare them for use in electrorefining. It would also be desirable to provide a process and apparatus which would allow the anode preparation processes to be done in a relatively small area, and to be done rapidly. Further, it would also be desirable to provide a process and apparatus that was suitable for automation in order to minimize worker involvement in a loud and potentially dangerous operation of handling, milling, grinding, and pressing the large and heavy anodes in rapid succession. Still further, it would be desirable to provide such a process and apparatus that could achieve production rates in excess of 300, and more preferably, in excess of 450 or 500 anodes per hour, or even higher.